An investigation into the determination of ammonium in mine bioleaching solutions utilising an ammonia gas electrode

Abstract

Fixed nitrogen is an essential nutrient for bacteria used in the mining industry to solubilise metals from their associated ores in a process known as bioleaching. Most bacteria are able to fix atmospheric nitrogen, but those which are not require a feed solution of aqueous ammonium to meet their nitrogen requirements. Bioleaching operations are large scale and therefore the cost associated with providing aqueous nitrogen is considerable. It is therefore important that only the minimum amount of aqueous nitrogen is added during the process to minimise costs. Camborne School of Mines were investigating the potential loss of aqueous nitrogen from bioleaching solutions through the precipitation of ammonium jarosite. In order to further their studies, they required development of a method for the determination of ammonium in a typical bioleaching solution so that they could research optimum bioleaching conditions to minimise loss of aqueous nitrogen. Various methods were researched and determination of ammonium using an ammonia gas selective electrode was investigated in detail. The method yielded promising results for determinations of ammonium between 0 and 50 mg/L in a typical bioleaching solution. Additions of base much in excess of ammonia electrode literature were required to liberate ammonia gas from bioleaching solutions, most likely due to the consumption of hydroxide during the precipitation of metal-hydroxide species. The performance characteristics of the method developed were assessed and the method and standard operating procedure developed were fit for purpose and adopted by Camborne School of Mines.